Elon Musk isn't a through and through science/engineering guy like, say, the founders of Intel, Sun, or Google. Elon Musk is best understood as a money man with a technical background, rather than a technical guy with money. He finds good ideas that have been sitting around, sometimes for decades, and pushes them to fruition through scale and radical cost cutting (which itself requires major technical advances). EVs, autonomous cars, solar panels, reusable rocketry, all of these have been worked on in California for a long time, but all of them cost too much for mass adoption. Elon Musk has made these things affordable to a much larger market.